High energy beams of neutral particles such as deuterium and tritium are of interest as fuels in controlled thermonuclear reactions such as fusion. To generate these intense high energy beams, ions are produced and accelerated to the required energy, then neutralized by stripping in a gas, metal vapor, or plasma jet. Negative ions are preferred since the neutralization efficiency is higher for negative ions than for positive ions at the energy levels of interest i.e., at energies greater than 100 keV.
Some experimental work has been performed to produce negative ions by preparing a target having a thick layer of an alkali metal, and bombarding the surface of the target with positive deuterium or tritium ions. Some of the positive ions interact with the target to pick up two electrons and then emerge upon reflection as negative ions. In another method, negative deuterium ions are produced by directing a flow of neutral deuterium atoms into a porous electrode containing a surface layer of barium oxide. Some of the neutral atoms pick up a single electron in passing through the electrode and then emerge as negative ions. Thus far, however, the negative ion currents achieved by these techniques have been impractically low. Formation and maintenance of the desired target surfaces has also proven difficult.
Accordingly, it is an object of the invention to provide a method and apparatus for producing negative ions.
It is a more particular object of the invention to provide improved methods and apparatus for producing negative deuterium or tritium ions in amounts suitable for use in controlled thermonuclear reactors.
It is also an object of the invention to provide apparatus for producing negative deuterium or tritium ions which includes an ionization electrode having a surface which is easy to form and reproduce.